An electromechanically operable disc brake of this type is e.g. disclosed in German patent application No. 195 11 287. The actuating unit of the prior art disc brake comprises an electric motor, an actuating element, and a reduction gear that is interposed between the electric motor and the actuating element and configured as a threaded roller pinion with a return arrangement of the threaded rollers. The friction lining associated with the actuating unit is moved into engagement with the brake disc by an axial displacement of the spindle of the threaded roller pinion. In the prior art disc brake, the actuating element is the spindle of the threaded roller pinion having a threaded nut which is driven by the electric motor to produce a corresponding tensional force. It is disadvantageous in the prior art electromechanically operable disc brake that the spindle is considerably loaded by transverse forces which are caused especially when large displacement travels occur (worn out Brake linings) and which are due to the effect of circumferential forces of the lining and the expansion of the brake caliper which occurs when the actuating unit is actuated.
Therefore, an object of the present invention is to improve an electromechanically operable disc brake of the type mentioned hereinabove to the end that the influence of disturbing forces and moments is eliminated.
According to the present invention, this object is achieved in that the spindle of the threaded roller pinion is drivable by the electric motor and the actuating element is provided by the threaded nut of the threaded roller pinion. An accordingly configured electromechanically operable disc brake is characterized by a high degree of efficiency and an extremely compact construction which is rendered possible by a very short and rigid design of the spindle permitting high mass-related brake torques.
To render the idea of the present invention more precise, the reduction gear is mounted in the brake caliper.
In a particularly favorable aspect of the object of the present invention, cam plates which cooperate with the threaded rollers are rigidly coupled to the spindle, and a groove is provided in the spindle which is used for the return of the threaded rollers.
To considerably reduce the necessary drive torque that is to be generated by the electric motor, the force transmission between the electric motor and the spindle is carried out by way of a planetary gear.
The sun wheel of the planetary gear is preferably the rotor of the electric motor. The planet pinions are in engagement with an internal toothing system, that is configured in the housing of the actuating unit and provides the hollow wheel of the planetary gear, and are arranged on a planet pinion carrier which cooperates with the spindle.
In another favorable aspect of the present invention, the force transmission between the rotor of the electric motor and the spindle is effected by way of a longitudinal shaft serration.
In another favorable embodiment of the present invention, a rotation-preventing mechanism is provided between the actuating element and the first friction lining. As a rotation-preventing mechanism, a lining-retaining spring can be used, for example, which is fitted to friction linings envisaged for application in hydraulically operable disc brakes.